This page is dedicated to the Siel Expander 80 synth module, which seems
to constantly be slated for being an inadequate copy of the Korg EX800.
This web page is a complete resource for the Siel Expander 80, showing
that if time is given to understand it, and accepting it's limitations,
then a very capable synth will become apparrent.

THE FACTS

The Italian company Siel released their DK80 synth keyboard in 1985,
which was a 12 voice analogue bitimbric (2 sounds at once) synth. The
Expander 80 was also released at the same time (costing only £399,
the cheapest instrument in it's class by a long way) being essentially
(but not just) half a DK80 - 8 voice polyphonic and one sound at a time.
Originally the Expander 80 was not supplied with a power supply, as the
DK80 one was designed to drive the pair (Siel expected the DK80 owner to
be the typcial owner of the Expander 80). The Expander 80 still retained
the 300 event two track sequencer, although both tracks have to play the
same sound. Similarities to the Korg EX800 cannot be ignored, especially
as the voice architecture and front panel layout do have similarities. The
Korg EX800 was released a year earlier in 1984, so the Siel Expander 80
definately followed it. Internally, they share no common electronics - so
it's no surprise they sound different

The Expander 80 architecture has 8 digitally controlled oscillators
(DCO), 9 VCA's (8 for the DCO's and one for the noise generator) and a
single 4-pole (24dB/octave) VCF (SSM2045), with nine 6-parameter digital
envelope generators (8 for the VCA's and one for the single VCF) plus 2
LFOs. A pink noise generator and analogue chorus are also included. A
double mode, stacks 2 DCO's together (4 note polyphonic) with detune -
though the DCO's have to share the same settings. In fact the oscillators
and VCA's are all on one chip (an M112 polyphonic sound generator), and
the envelopes are under microproccesor control (a Texas TMS7000 in case
you were wondering). The chorus is an analogue bucket brigade delay line
(TDA1022).

The M112 chip conatins a top octave generator with octave dividers, 5
footage outputs under VCA control, this is organ frequency divider
technology rather thna synth voltage control technology, though it still
remains analogue voice generation.

The Expander 80 block diagram:

LIMITATIONS

OK - the Expander 80 is not perfect, it has one major economy in it's
design, which it shares with the likes of the Korg Mono/Poly, Poly 800,
EX800 and also the Moog Opus 3 (so it's not alone) - it only has one VCF.
If playing single notes (monophonic playing) no issue, if playing block
chord stabs - no issue, but trying to play two hands at once will mean
either notes not sounding again, or all notes retriggering with each new
note played. The Expander 80 has a trigger mode for the user to decide
which mode is best. There are some sounds when this retriggering effect
can become a useful part of the sound, so it is not always a limitation!

The Expander 80 has 40 preset sounds (memories 00 - 39) and (only?!) 10
programmable sounds (memories 40 - 49). If memories 50-99 are selected,
memory location selected minus 50 is called up. Extra memory is available
on the optional (and very rare!) RAM cartridge, where a further 50 memory
locations are available (memories 50 -99 with the Cartridge mode enabled).
Siel did (or maybe were going to - has anybody ever seen a Siel ROM
cartridge?) produce a preset ROM cartridge with 100 sounds on in two banks
of 50.

ODDITIES

Like any synth there are oddities of the system, and the Expander 80 is
no different here. One apparent feature of the oscillators, is that there
appears to be four of them per note! Yes, so it will seem. There are eigth
oscillators (8 note poly single mode), and by stacking two under each key
(4 note poly double mode), but each oscillator can be "detuned"
to fatten it up. If put into whole mode - that is, using 8 note polyphony
and one oscillator, the detune fine parameter still introduces a two
oscillator detune effect. Then, putting the Expander 80 into Double mode
using 4 note polypony and two oscillators, the detune fine works on this
as well. DCO2 can be transposed chromatically anywhere up to nearly 5
octaves higher than DCO1 - both DCO's have detune - it's definately like
having 4 oscillators. But - what is really happening is simply the chorus
effect. There is no oscillator detune fine in the Expander 80 at all, as
the detune fine simply brings in 15 levels of chorus, in fact the
oscilators cannot be fine detuned, only in chromatic intervals.

As the detune fine is actually the chorus effect, this means that the
DCO detune and the Chorus effect are exclusive. When the Chorus is
switched on, the detune becomes unavailable. When the chorus is acting as
"detune", the chorus is mono output, though when it is used as a
conventional chorus, it's output is stereo.

Stereo output? Well, the Expander 80 does have two outputs - not that
there is much stereo about it though. Unlike it's keyboard brother - the
DK80 - which being bitimbric could put a different sound to each output
(allowing various auto panning effects), the one sound at a time Expander
80 can only put the same sound to both outputs. The Chorus effect is
however stereo, though only by inverted phase on one side.

Who printed the panel wrong then? Parameter 21 (Detune Interval) goes up
to a value of 61 - and not just 11 shown on the panel (this is a
limitation of the DK80). Parameter 93 (MIDI Channel) goes up to a value of
16 - and not just 15 shown on the panel.

The Expander 80 has a slightly odd (complete with bugs) System Exclusive
implementation, there seems to be no official data on the implementation,
but it does support bulk dumps and dump request, though it does not seem
to support parameter changes via sys ex, it does however allow parameter
changes by MIDI controllers.(see below for MIDI control data). The only
editor known is for Soundquest's Midiquest. (Though there was a Siel's own
Commodore 64 editor back in the 1980's). This is what the Midiquest editor
looks like:-

There seems to be a bug in the MIDI controller reception with the
Expander 80, unless there ever was an operating system update, Parameter
22 (Detune Fine) and Parameter 81 (Chorus) cannot be controlled by their
associated controllers (CC30 and CC62). When receiving MIDI CC30, the
Expander 80's display changes to show the incoming data, but the actual
detuning (chorus speeed) does not change, same with CC62. Maybe this was
corrected in a software revision.

UNDOCUMENTED THINGS....

The Expander 80 allows every parameter to be controlled by MIDI
controllers, though Siel never told you what they were, so here they are:-

Parameter

Function

MIDI CC

Range

Parameter

Function

MIDI CC

Range

Parameter

Function

MIDI CC

Range

01

DEG VCA-A Attack

12

0 ~ 15

11

DEG VCA-B Attack

21

0 ~ 15

21

Detune Interval

29

0 ~ 61

02

DEG VCA-A Decay

13

0 ~ 15

12

DEG VCA-B Decay

22

0 ~ 15

22

Detune Fine

30

0 ~ 15

03

DEG VCA-A Breakpoint

14

0 ~ 15

13

DEG VCA-B Breakpoint

23

0 ~ 15

23

Noise Level

31

0 ~ 15

04

DEG VCA-A Slope

15

0 ~ 15

14

DEG VCA-B Slope

24

0 ~ 15

24

Noise Destination

32

1 (VCA) ~ 2 (VCF)

05

DEG VCA-A Sustain

16

0 ~ 15

15

DEG VCA-B Sustain

25

0 ~ 15

06

DEG VCA-A Release

17

0 ~ 15

16

DEG VCA-B Release

26

0 ~ 15

07

DEG VCA-A Dynamics

18

0 (Off) ~ 1 (On)

17

DEG VCA-B Dynamics

27

0 (Off) ~ 1 (On)

08

DEG VCA-A Damper

19

0 (Off) ~ 1 (On)

18

DEG VCA-B Damper

28

0 (Off) ~ 1 (On)

09

DCO Mode

20

1 (Whole) ~ 2 (Double)

Parameter

Function

MIDI CC

Range

Parameter

Function

MIDI CC

Range

Parameter

Function

MIDI CC

Range

31

DEG VCF Attack

33

0 ~ 15

41

LFO-2 Frequency

40

0 ~ 15

51

LFO-1 Frequency

46

0 ~ 15

32

DEG VCF Decay

34

0 ~ 15

42

LFO-2 Final Level

41

0 ~ 15

52

LFO-1 Final Level

47

0 ~ 15

33

DEG VCF Breakpoint

35

0 ~ 15

43

LFO-2 Initial Level

42

0 ~ 15

53

LFO-1 Initial Level

48

0 ~ 15

34

DEG VCF Slope

36

0 ~ 15

44

LFO-2 Delay Time

43

0 ~ 15

54

LFO-1 Delay Time

49

0 ~ 15

35

DEG VCF Sustain

37

0 ~ 15

45

LFO-2 Delay Mode

44

1 (Manual), 2 (Auto)

55

LFO-1 Delay Mode

50

1 (Manual), 2 (Auto)

36

DEG VCF Release

38

0 ~ 15

46

LFO-2 Waveform

45

1 (Triangle), 2 (Square)

37

DEG VCF Dynamics

39

0 (Off), 1 (On)

Parameter

Function

MIDI CC

Range

Parameter

Function

MIDI CC

Range

Parameter

Function

MIDI CC

Range

62

DCO Waveform

51

0 (Off), 1 (Sqr), 2 (Saw)

71

VCF Cutoff

57

0 ~ 99

81

Chorus

62

0 (Off), 1 (On)

63

DCO Sawtooth Octave

52

1 (16'), 2 (8'), 3 (4')

72

VCF Resonance

58

0 ~ 15

82

Volume

63

0 ~ 15

64

DCO Square 16' Level

53

0 ~ 15

73

VCF Keyboard Track

59

0 (Off), 1 (Half), 2 (Full)

65

DCO Square 8' Level

54

0 ~ 15

74

VCF DEG Trigger Mode

60

1 (Single), 2 (Multi)

66

DCO Square 4' Level

55

0 ~ 15

75

VCF DEG Level

61

0 ~ 15

67

DCO Square 2' Level

56

0 ~ 15

If the Expander 80 ever displays 4c at switch on, this means the
internal backup battery has gone.

MIDI Controller 65 is the Manual LFO trigger control, this is a hang
over from the DK80 keyboard version, that had a trigger switch (rather
than a mod wheel). Controller 65 is usually the second pedal function
(although perhaps the standard controller CC1 would have made more sense -
never mind.....)

The three envelopes share the same timings, the Attack and Decay times
are variable from 30mS to 6 seconds. This minimum 30mS attack time
explains why the Expander 80 does not have an aggressive punchy sound. The
Slope and Release times go from 60mS to 21 seconds, which should be
adequate for everything.

The two LFO's share the same spec as well, both ranging from 0.25Hz at
it's slowest to 10Hz fastest. The delay time variable from zero to 1.5
seconds. The LFO trigger mode is always Single (the Trigger Mode parameter
74 does not affect the LFO trigger). The LFO's are not key synced, so free
run at all times. In case your curious, here is the LFO speed reference:

LFO Frequency Setting

LFO Frequency

0

0.25 Hz

1

0.5 Hz

2

0.75 Hz

3

1.25 Hz

4

1.5 Hz

5

2 Hz

6

2.5 Hz

7

3 Hz

8

3.5 Hz

9

4 Hz

10

4.5 Hz

11

5 Hz

12

6 Hz

13

6.5 Hz

14

8 Hz

15

10 Hz

RELIABILITY

Do they ever go worng? Well yes they do, but so do many vintage synths,
the most common problem seems to be the power supply itself, whether they
just get lost or blow up is unclear, but many Expander 80's don't have the
original power supply, and Expander 80's often turn up without any power
supply. The power supply needs to be AC (not DC) and has to be centre
tapped 16-0-16 (anything from 15-0-15 to 18-0-18 is OK, but don't go above
18v as an unregulated line is connected to the display). The transformer
needs to be 1A and connected to a 5 pin (Domino) DIN socket with the
middle pin being the common (ground) and the outer pins carrying the AC.

Battery failure is likely by now if it hasn't already been changed,
although a standard CR2032 is needed it uses a soldered in holder, so a
soldering iron is needed to change it.

TWEEKS.

I am not a fan of modifying things, a synth is what it is, if it's not
what you want - get a differenent one! So, consider this as calibration.
The resonance on the filter is not normally set very aggresive. Remember
that on the Expander 80, the VCF comes after the VCA, so if the VCF goes
into self oscillation, nothing will stop it sounding. Though, the
resonance can be optimised by a single internal adjustment. This needs to
be done with the Expander 80 apart and switched on, there is no great
danger in this, as the Expander 80 does not have any mains inside, the
highest voltage is the 16-0-16 AC input, but take care you could still
harm the Expander 80.

Here is a step by step guide to getting the filter resonance optimised.
First disconnect the Expander 80, turn it upside down on a soft surface.
Take out the 6 screws at the edges (you'll need a thin philips screwdriver
to reach into the deep recess). The next stage is to loosen the three
output jack socket nuts (out L,R and phones), you don't need to take the
nuts off, but you can if you prefer. With the Expander the right way up,
gently part the two halfs so that the hinge action is to the front. You
will be able to lay both halves flat side by side.It should look like
this:

Now having laid it all out nicely, you are going to need to lift the
front up so you can operate it. Connect an audio out so you can hear
what's going on and apply the power, you don't need MIDI for this
adjustment. Set the VCF cutoff to around 60 (if it's too high you won't
hear it), set the resonance to maximum 15 (this is vital). Now locate the
internal resonance adjuster P4, this is located at the back and centrally
on the analogue board (the one with the output sockets on). With a small
flat blade screwdriver adjust P4 slowly until you here the filter self
oscillate, then back it off slightly so you cannot hear it. That is it!
Put it all back together it's done. You will find the presets sound
better, and that filter will really zap now - it's an SSM 2045 filter, so
it should sound as good as this.

PEDIGREE

The oscillators/VCA's are the M112 chip, perhaps not pedigree, as this
chip was designed for use in organs, but the SSM filter is the SSM2045 as
used in the Emu Emulator II, and SSM filters (mainly the SSM 2044) are
used in the Fairlight CMI II, Korg Poly-6/Monopoly, PPG Wave 2.2/2.3,
Kawai K3/SC240 and Simmons SDS5 etc. The early Sequential Prophet V's used
SSM 2040's as well as the RSF Kobol.